Antarctica Adventure 2004 

Long Term Ecological Research (LTER)

A view of Palmer Station.

The life processes within each ecosystem can last days, seasons or tens of thousands of years. What the 24 LTER sites are researching is the composition of those ecosystems, their structure and functions and their relationship to climate over long periods of time (decades to millennia). LTER sites range from deserts, marshes, forests and grasslands to alpine and polar ecosystems.

Another distinctive characteristic of LTER is the length of time scientists make observations at each site. While the average research grant in the United States lasts for three years and usually isn’t renewed, LTER grants last for six years and can be renewed indefinitely. If all goes according to plan, the LTER program will continue into the next century and possibly beyond. Ducklow is one of the first Palmer Station Long Term Ecological Research (PAL LTER) scientists, but he certainly won’t be among the last. For example, because LTER was launched in 1980 with six sites some projects are now into 20 years of sustained observation; PAL LTER has logged a solid decade of regular observations.

Palmer Station Long Term Ecological Research (PAL LTER)

Antarctica is an ideal place to study climate change. One of the most distinguishing features of its marine ecosystem is sea ice, which forms annually in the austral (southern) autumn and winter (April to June) and covers an area around the continent during the winter about the size of the lower 48 United States. Sea ice is formed from freezing seawater, while glacier ice comes from snow. It melts and retreats in the austral spring (October and November). The central tenet of PAL LTER is that the annual advance and retreat of sea ice plays a major role in determining the spatial and temporal changes in the structure and function of the Antarctic marine ecosystem.

Glaciers at Rothera Station.

The entire ecosystem is centered in and dependent on sea ice. The ice regulates light supply to phytoplankton (microbial plant life like algae) that form the basis of the food chain, provides a habitat for juvenile krill (shrimp-like animals) and affects the feeding and breeding of penguins and seals. There is even a special community of microorganisms that lives in the sea ice itself—an entire ecosystem virtually unknown 30 years ago that’s the size of North America.

In the beginning, PAL’s research examined the relationships between several critical populations of organisms and the advance, size and retreat of the sea ice: phytoplankton and bacteria; the Antarctic krill, Euphausia superba; and the Adélie penguin, Pygoscelis adelia. The Adélie, one of just two Antarctic-only penguins, is wholly dependent on, and is a year-long resident of the Antarctic sea-ice ecosystem (the other is the Emperor penguin, the only bird that never needs to set foot on land). Adélies are the most abundant penguins in Antarctica.

Sea ice along the Antarctic Peninsula undergoes approximately a six to ten year cycle of change between years of minimum and maximum area related to global-scale climate patterns like El Nino. The maximum and minimum coverage differs by about twofold in area. “High ice” years are followed by greater than average photosynthesis by phytoplankton, larger krill populations and more penguin chicks. In “low-ice” years the opposite tends to be true. Although Ducklow and the other PAL scientists have demonstrated this general pattern over a full cycle of high-low-high ice years, identifying the mechanisms involved and understanding exactly WHY it happens is unknown. They are almost certain it is related to the connection between variations in sea ice cover (a “physical driver” of ecosystem functioning) and phytoplankton productivity. The rest of the food web flows from this base.

Besides understanding the sea-ice ecosystem over the decades, PAL scientists are also investigating the ecosystem’s longer-term responses to climate change. PAL LTER established that the West Antarctic Peninsula (WAP) has experienced steady warming in the past 50 years. The average wintertime temperature has increased by almost 6° Celsius (10°F) since 1950. The overall average temperature has increased 2 to 3°C in the same period. This is one of the most rapid rates of warming anywhere on earth, and for an ecosystem poised near the freezing point of seawater (-1.8°C), ultimately catastrophic if the warming continues.

PAL has also established a statistical relationship between the warming trend and another trend, the shrinkage of the annual sea ice cover. The sea ice now lasts for a shorter period each year and covers a smaller area in the WAP than it did 25 years ago. With the long-term warming trend, the WAP is warmer and moister in the north and colder and drier in the south. The Palmer Station region right now stands in the middle of this climate gradient, but getting warmer. As warming proceeds, the warm conditions of the north are migrating down the Peninsula, past Palmer and toward the continent proper. What are the implications of these trends for the ecosystem? ...more